T L Audio
User Manual
Ebony Series A1 Dual Pre-Amp
TL Audio Limited, Letchworth, England.
Tel 01462 492090, Fax 01462 492097.
www.tlaudio.co.uk email: info@tlaudio.co.uk
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TABLE OF CONTENTS
TABLE OF CONTENTS.............................................................................................................................. 1
INTRODUCTION ......................................................................................................................................... 2
WHY CLASS-A?............................................................................................................................................ 2
WHY TUBES? ................................................................................................................................................3
WHY BALANCED I/O?..................................................................................................................................3
THE A1 DUAL PRE-AMP. ............................................................................................................................. 3
PRECAUTIONS ............................................................................................................................................5
BLOCK DIAGRAM...................................................................................................................................... 6
INSTALLATION........................................................................................................................................... 7
AC Mains Supply. .................................................................................................................................... 7
Audio Inputs. ............................................................................................................................................ 7
Instrument Inputs..................................................................................................................................... 8
Outputs. ....................................................................................................................................................8
Ventilation................................................................................................................................................ 8
OPERATION. ................................................................................................................................................ 9
Microphone Input .................................................................................................................................... 9
Instrument Input ...................................................................................................................................... 9
Input Gain. ............................................................................................................................................... 9
30dB Pad Switch...................................................................................................................................... 9
Phantom Power. ...................................................................................................................................... 9
Tube Stage Drive and Peak LEDs........................................................................................................10
Output Peak LED. .................................................................................................................................10
GETTING STARTED ................................................................................................................................11
Mic Input:...............................................................................................................................................12
Instrument Input: ...................................................................................................................................12
High Pass Filter: ................................................................................................................................... 12
Output Gain:..........................................................................................................................................12
Output: ................................................................................................................................................... 12
Tube Stage: ............................................................................................................................................13
Metering:................................................................................................................................................13
Power Requirements: ............................................................................................................................13
Dimensions: ...........................................................................................................................................13
SERVICE ...................................................................................................................................................... 14
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INTRODUCTION
New from TL Audio, The Ebony Series is a sleek looking range of discrete Class A
processors designed to heighten your audio experience.
The range consists of 3 units, all of which use Discrete Class A circuitry and have an
optional tube stage with variable drive putting you in control of how ‘creamy’ or how
‘cool’ your unit sounds.
Hand assembled in England to the highest standards, the Ebony uses stylish, quality
chrome knobs together with a high gloss black finish to make the exterior look just as
smooth as the circuits sound.
The Ebony Series have all the features you come to expect with TL Audio, including
balanced I/O, multi input options, analogue VU metering and intuitive, precise
controls.
All units are also compatible with the TL Audio DO-2 digital SPDIF interface for easy
digital connectivity with high quality conversion.
A combination of supreme quality, unrivalled sound and stylish aesthetics - this range
offers superior analogue processing to accompany a digital world.
Why Class-A?
Class A circuits are designed with a constant current flowing through all of the
transistors, which is sufficient to drive the peak output required from each block of the
circuit. This ensures that every transistor is kept at its optimum operating point,
minimising non-linearities due to changes in current and internal thermal effects, and
eliminating the objectionable “cross-over” distortion typical of class AB circuits.
Due to the higher steady state (or “quiescent”) currents used, the power dissipation of
class A circuits is substantially higher than can in general be handled by integrated
circuits. It is also possible to design discrete transistor circuits to operate at higher
voltage rails than are available for audio integrated circuits, adding the benefit of
greater headroom and improved dynamic range. For these reasons, there are no
integrated circuits in the audio paths of the Ebony Series.
The outstanding audio quality is reflected in the technical specification of the units, with particularly
low noise and distortion, and wide frequency response.
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Why Tubes?
Valves - or “Tubes” - have long been associated with excellent audio quality,
recognised as adding “warmth” or “depth” to a signal. Driving the valves harder
results in an increasing level of mainly second harmonic distortion, which is
responsible for the characteristic overdriven valve sound.
The Ebony Series feature variable drive valve circuits, which may be switched into the
audio paths, or bypassed completely. The valve drive control varies the signal level
through the valve stage, without affecting the overall gain from input to output. It is
therefore possible to vary to the degree of harmonics added by the valve, from subtle
warming to crunchy overdrive, with a single control. The signal level through the
valve is displayed by the variable intensity “Drive” LED and the “Peak” LED.
Where instrument inputs are present on the Ebony models, dedicated valve input
stages are used. Switchable to high or low sensititivity (and impedance), these input
stages represent the ultimate quality for the first stage of instrument amplification.
Why Balanced I/O?
Balanced I/O (Inputs and Outputs) are always preferable to unbalanced connection in
an audio system. A balanced signal consists of signal phase and non-phase
connections, which form a differential pair, independent of the ground (or earth)
connection. Noise, particularly mains hum and high frequency interference can often
be present in unbalanced systems due to small differences in ground potential or
circulating ground currents (“loops”) between units, where the signal phase (only) is
taken as an absolute value with respect to ground.
A correctly designed balanced interface should have both phase and non-phase signals
of equal magnitude (and source impedance), but should allow either of the phase and
non-phase signals to be connected to an arbitrary electrical point (e.g. ground) without
changing the differential level. Therefore, if, for instance, the non-phase signal is
shorted to ground by an unbalanced input on a piece of equipment, then the phase
signal should double in magnitude to compensate. Such an arrangement is referred to
as “floating” or “ground-free”. Balanced signals require 3 pin connectors, such as
XLR’s or TRS jack plugs, carrying the phase and non-phase signals, plus a screening
ground connection.
Naturally, the Ebony Series features balanced, ground-free signals for all line inputs
and outputs, as well as insertion points where present. The range is also compatible
with unbalanced equipment, as described above.
The A1 Dual Pre-Amp.
The Ebony Series A1 Pre-Amp features two independent channels, with each channel
offering mic and instrument inputs.
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The block diagram of one of the channels is shown in fig.1. A discrete Class A
electronically balanced mic input amplifier is used, delivering superior audio
performance with very low noise, low distortion and wide bandwidth. The mic input is
suitable for low impedance (150-600 ohm) microphones, with a gain control range of
+16 to +60dB. Front panel switches provides 48V phantom power, and 30dB pad for
high output mic applications.
The front panel mounted jack socket is suitable for a variety of sources, including
electric guitar, acoustic pickup and keyboard. The instrument input has high/low
switching, and a dedicated valve input stage.
Phase reverse and high pass filter switches are provided, affecting both mic and
instrument inputs.
The tube stage has a variable drive control, with the signal level indicated by the
variable intensity “Drive” LED and “Peak” LED. Use of this feature typically
introduces 1% to 10% harmonic distortion, predominately second harmonic, without
changing the output level from the unit. The tube stage can be selected or bypassed as
required.
A VU meter is provided, which can be selected to either channel, and input or output
signals. The meter is also provided with a “+10dB” switch, which keeps the reading
on the scale when driving a high level out (to a DAW, for example). In the +10 mode,
0VU is calibrated as +14dBu out.
Please read this manual fully before installing or operating the Pre-Amp.
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